Beta acids, also known as lupulone, are a constituent of hops, often up to 5-7%. In the normal brewing process, in which hops are added at the kettle during the boiling of the wort, they remain unconverted to useful substances except for a small percentage oxidizing to hulupones. The greater amount is either lost to the trub or deposited on the yeast, beta acids in themselves being very insoluble in beer.
Worden, U.S. Pat. No. 3,552,975, describes a process for converting beta acids into 4-desoxy alpha acids, by hydrogenolysis at a pH preferably less than 1. These in turn are oxidized to form tetrahydroalpha acids, which may be isomerized to tetrahydroisoalpha acids, or further reduced and isomerized to hexahydroisoalpha acids as shown by Worden. Both types of reduced isoalpha acids have been found useful in the making of light-stable beer.
There was, in the past, speculation that hops may have helped control brewhouse bacterial infections due to the presence of hop acids in the wort and beer. However, since the hop beta acids are not found in beer, such control, if it indeed existed, must have been due to the hop alpha acids and isoalpha acids. Beta acids are known to be highly unstable, being oxidized in the boiling wort to bitter hulupones and by themselves to deteriorate in a matter of days or hours after crystallization. This lack of stability is now shown to be overcome by conversion to hexahydrolupulone (hexahydro beta acids). Since there is a vast excess of lupulone available as a result of being discarded in the brewing process, it is a potentially cheap raw material.
Furthermore, as a derivative of a generally-recognized as safe hop extract, hexahydrolupulone can be considered negligibly toxic when ingested.
Our copending application, Ser. No. 232,289, describes a process for removal of catalyst poisons from natural beta acids, by treatment with a polyvalent metal ion other than palladium or platinum, to produce a purified aqueous beta acid solution, which purified solution is crucial to the making of hexahydrolupulone according to the present invention. In addition, the Examples of this application describe the appropriate conditions for the hydrogenation of the purified beta acids, which are distinctly different from the conditions required and described in our previous application and earlier by Worden to achieve hydrogenolysis. That objective was a totally different product, 4-desoxy alpha acids, which require the removal of an isoprenoid side chain from the beta acids by hydrogenolysis. Hexahydrolupulone does not have any side chains removed, but rather the existing isoprenoid side chains are all hydrogenated, three (3) moles of hydrogen being required for each mole of starting beta-acids. The critical hydrogenation conditions described prevent the hydrogenation of the ethylenic linkages in the ring and the reduction of the keto groups .